Questions And Answers

A PCB we are manufacturing has a lithium battery installed. In the application note from the battery manufacturer under shipping and handling it states "Never ship completed circuit boards with installed batteries in anti-static bags as the bags are conductive and will short out the battery." How would you recommend handling these PCB with batteries installed? -Anonymous, Ogdensburg, New York

Answer

I can see why the manufacture is stating that, there probably have been some instances where this may have occurred, but I believe the probability would be rather low. A good metal-in shielding bag may have an inner [bag] resistance of 1 to 100 megohms and if say the ground plane and the ungrounded battery terminal were to come into physical contact, there may be a leakage current that could eventually drain the battery. On the other hand, a good metal-out shielding bag has an inner surface resistance of less than 1x1012 ohms and typically 1x1011 ohms, a little less than twice that of a metal-in shielding bag. Any circuit established with the battery and bag in included would be hard pressed to have any significant current flow. This might be the alternative ESD protection for your boards with lithium batteries installed. The other suggestion, would be to remove the battery (if possible) and have the customer install it when the board was installed into its application.